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Occupational hearing loss is one of the most common occupational illnesses in the United States. When control technologies have not eliminated hazardous noise exposures or are not feasible, using personal hearing protection devices (HPDs) becomes the only true means of protecting a worker. Currently, there is no requirement that HPDs be fit-tested in the workplace, partially because hearing protector fit-testing technology has historically been impractical for use in the field. To address this issue, the National Institute for Occupational Safety and Health (NIOSH) developed a hearing protector fit-testing system called HPD WellFit(TM). The portable PC-based system is fast, accurate, and can be used as a stand-alone instrument in any workplace setting or as part of an annual audiometric monitoring or hearing conservation program. NIOSH is actively field testing HPD Well Fit(TM) with the US Army, the US Department of Interior (Bureau of Reclamation), and several universities.